If 5th January 2011 was a Thursday, then what day of the week was it on 1st January 2013?

Let's count the number of days or odd days between 5th January 2011 and 1st January 2013.First, find the day on 5th January 2012:2011 is an ordinary year (365 days = 1 odd day).So, 5th January 2012 will be $\text{Thursday}+1=\text{Friday}$.Next, find the day on 5th January 2013:2012 is a leap year because it is divisible by 4, and it includes February 29 between January 2012 and January 2013. A leap year has 2 odd days.So, 5th January 2013 will be $\text{Friday}+2=\text{Sunday}$.Now, count backward from 5th January 2013 to 1st January 2013:5th January 2013 = Sunday4th January 2013 = Saturday3rd January 2013 = Friday2nd January 2013 = Thursday1st January 2013 = WednesdayTherefore, 1st January 2013 was a Wednesday.